Circuit breaker trip assembly with increased compensation for misalignment



Feb. 21, 1967 STROBEL 3,305,653

A. v CIRCUIT BREAKER TRIP ASSEMBLY WITH INCREASED Filed June 21, 1965 COMPENSATION FOR MISALIGNMENT 6 Sheets-Sheet 1 A. STROBEL 3,305,653

TRIP ASSEMBLY WITH INCREASED Feb. 21, 1967 CIRCUIT BREAKER COMPENSATION FOR MISALIGNMENT Filed June 21, 1965 6 Sheets-Sheet 2 A. STROBEL TRIP ASSEMBLY WITH INCREASED 6 Sheets-Sheet 5 Feb. 21, 1967 CIRCUIT BREAKER COMPENSATION FOR MISALIGNMENT Filed June 21, 1965 Feb. 21, 1967 A. STROBEL ,3

CIRCUIT BREAKER TRIP ASSEMBLY WITH INCREASED COMPENSATION FOR MISALIGNMENT Filed June 21, 1965 6 Sheets-Sheet 4 BY 17,644 F/VA', 62 552, Q92 9; Jh F-n Feb. 21, 1967 Filed June 21, 1965 A. STROBEL CIRCUIT BREAKER TRIP ASSEMBLY WITH INCREASED COMPENSATION FOR MISALIGNMENT 6 Sheets-Sheet 5 Feb. 21, 1967 A. STROBEL CIRCUIT BREAKER TRIP ASSEMBLY WITH INCREASED COMPENSATION FOR MISALIGNMENT 6 Sheets-Sheet 6 Filed June 21, 1965 United States Patent O 3,305,653 CIRCUIT BREAKER TRIP ASSEMBLY WITH IN- CREASED COMPENSATION FOR MISALIGN- MENT Albert Strobe], Cherry Hill, N .J., assignor to I-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Filed June 21, 1965, Ser. No. 465,304 Claims. (Cl. 200116) My invention relates to molded case circuit breakers in general and more particuuarly to replaceable trip unit assemblies therefor which are constructed to provide increased relief compensation in the event of misalignment between the cooperating mounting means of the trip unit assembly and the circuit breaker frame unit. Specifically, the instant invention relates to an improvement over a trip unit assembly of the type having an indirectly heated bimetal as shown in U.S. Patent No. 3,139,497 entitled Thermal Shunt for Trip Unit, issued June 30, 1964, in the name of George J. Giessner, and assigned to the assignee of the instant invention.

Molded case circuit breakers of the larger frame size are often-times provided with removable and replaceable trip units. That is, the overall circuit breaker assembly is formed of two principal cooperating assemblies. The main assembly includes: the cooperating contacts for each of the phases; the general operating mechanism for moving the contacts between their engaged and disengaged positions, either manually or automatically responsive to predetermined load conditions; and the line and load terminals. A region is provided in the main assembly for the convenient reception of the trip unit assembly. The trip unit assembly is an integrally contained assembly and includes a conductive terminal strap for each of the phases. The terminal straps are both mechanically and electrically connected to cooperating current carrying members of the circuit breaker frame so as to complete the current path therethrough. The trip assembly also includes individual current sensing means for each of the phases, which, upon their actuation, typically rotate a trip-per bar to unlatch the general operating mechanism of the circuit breaker.

The current sensing means provided within the trip unit assembly usually includes both a magnetically actuatable or instantaneous trip, responsive to excessive overload conditions, and a thermally actuatable, or time delayed trip, responsive to prolonged moderate overload conditions. The thermally actuatable element, which may typically be an elongated bimetal, is fixedly mounted at one end to a mounting frame of the trip unit assembly, as well as being interconnected to the terminal strap for sensing of the current magnitude flowing therethrough.

Under normal manufacturing tolerances it is anticipated that a predetermined degree of misalignment will be experienced between the cooperating mounting means of the trip unit assembly terminal strap and the current carry-ing members of the circuit breaker frame assembly. Should there be a completely rigid interconnection between these two assemblies and the thermally responsive element, the stress forces resulting from such misalignment will be directly transmitted to the thermally responsive element. Such stress 'forces will disadvantageously affect the calibration accuracy of the thermal element. Accordingly, it is necessary to provide some relief compensation for such misalignment between the trip unit assembly and the circuit breaker frame in a manner which will substantially avoid transmission of the stress forces to the thermally responsive tripping element.

In some prior art circuit breakers of this type, it had been the practice to construct the terminal straps themselves of either a thin enough material to be flexible or of several laminations of thin material. However, this will severely limit the current rating of the circuit breaker, inasmuch as the resistance of the terminal strap will be increased, thereby resulting in excessive heating of this portion of the circuit breaker current path. This limitation has become particularly critical in present-day circuit breakers wherein the trend has been to reduce the frame sizes while increasing their ratings. In order to effect such a reduction of size it is necessary to reduce the resistance path through the circuit breaker to an absolute minimum.

A partial solution to he problem is shown in aforementioned Patent No. 3,139,497, wherein the terminal strap is constructed of a solid member, but the connection to the thermally responsive element is provided by a flexible thermal shunt which will still provide good heat transfer from the heater portion of the terminal strap to the bimetal. The shunt is typically constructed of a plurality of copper laminates to allow some movement of the terminal strap relative to the trip unit mounting frame. Such movement does provide some compensation for misalignment. In that structure, however, the thermal shunt is mounted flush against the top surface of the terminal strap, with such mounting serving to limit the degree of misalignment that may be accommodated by the flexible shunt member. The instant invention constitutes an extremely simplified modification thereof which will permit appreciably increased compensation relief against such misalignment derived stress forces.

Basically my invention provides a thermally conductive spacer plate interposed between the thermal shunt and the connecting surface of the terminal strap. The provision of such a thermal spacer plate will permit substantially increased flexibility, resulting in compensation for both lateral and vertical misalignment between the trip unit assembly and the circuit breaker frame.

Thus, wherein the structure shown in aforementioned U.S. Patent 3,139,497 will essentially provide relief for misalignment in a lateral direction only, the instant inven tion, by the provision of an additional spacer member, provides increased relief against misalignment derived stress forces in the vertical direction also, while still permitting effective heating of the bimetallic member by the thermal shunt connection.

It is therefore seen that a primary object of my invention is to provide an improved circuit breaker trip unit construction which will compensate for appreciable misalignment with respect to the circuit breaker frame mounting without transmitting stress forces to the bimetal.

Another object of the instant invention is to provide an indirectly heated bimetal connected to a terminal strap by a flexible thermal shunt, with such thermal shunt being space-separated from the surface of the terminal strap a predetermined amount to provide increased relief against misalignment.

Still another object of the instant invention is to provide a replaceable trip unit assembly for use in conjunction with a multi-phase circuit breaker unit, wherein misalignment between the mounting of the trip unit assembly and the circuit breaker frame is compensated for in an improved manner by the connection between the bimetallic element and current carrying thermal strap of the trip unit assembly.

An additional object of this invention is to provide such a trip unit assembly wherein the bimetallic element is rigidly connected to the trip unit mounting frame, and connected to the terminal strap via a thermal shunt, spaceseparated from the terminal strap by a thermally conductive spacer member.

These as well as other objects of my invention shall become readily apparent upon reading the following description of the accompanying drawings, in which:

FIGURE 1 is a perspective view of a three-phase molded case circuit breaker construction which may be used in the practice of the instant invention, and wherein the cover is removed to reveal the internal mechanism thereof;

FIGURE 2 is a plan view with the cover replaced and partially cut away of the circuit breaker shown in FIG- URE 1;

FIGURE 3 is a longitudinal cross-section view taken through the center phase along the arrows 3-3 as shown in FIGURE 2;

FIGURE 4 is a cross-sectional view along the lines 4-4 of FIGURE 1 and showing the trip unit assembly;

FIGURE 5 is a top view of FIGURE 4 showing the trip unit assembly, partially broken away in cross-section;

FIGURE 6 is a side elevation view of a portion of one phase of the trip unit assembly, and showing in dotted lines the substantial degree of misalignment which may be compensated for by the additional spacer member of the instant invention; and

FIGURE 7 is an exploded perspective view showing the thermal sensing trip portion of the trip unit assembly.

Now referring to the figures; circuit breaker 10 wherein my invention is incorporated, is typically shown as. a commercially available three-phase molded case unit. It should be naturally understood that the novel concepts of my invention may be incorporated in numerous other frame sizes and types, with this embodiment being merely for illustrative purposes. The unit is assembled within a housing comprising molded base 11, separated into corripartments 12, 13, and 14, respectively, for locating the operating members of each of the phases. The adjacent compartments are separated by housing walls and 16. Main cover assembly 17 and end covers 18 similarly include barriers for maintainingthe longitudinally extending compartments of the housing, with end shields 19 being located at the line and load ends of the circuit breaker 10. i i

The current carrying members of all three phases are identical so that for the sake of brevity only one of the sets of elements, such as the center phase as shown in FIG- URE 3 will be described. The current path between the line terminal strap 20 and load terminal strap 21 proceeds from stationary contacts 22 and 23 to movable contacts 24 and 25 carried by contact arms 26 and 27 through flexible braids 28, contact carrier strap 29 and trip unit strap 102.

Since circuit breaker 10 is of a relatively high current carrying capacity, contacts 22-24 function as arcing contacts and are properly situated to move into engagement and disengagement within the opening defined by circuit breaker arc chute assembly 31. The arcing contacts 22- 24 are shown paralleled by two sets of main contacts 23-25. The main movable contacts 25 are each mounted to individual contact arms 27, each connected by an individual section of braid 28 to contact carrier strap 29, while cooperating stationary contacts 23 are mounted to line terminal strap 20. The movable arcing contact 24 is similarly mounted to its contact arm 26, which is connected by a braid section 28 to the strap 29. Its cooperating stationary contact 22 is also mounted to line terminal strap 20. The contact arms 26-27-26 of each phase are, in turn, pivotally mounted by rod 36 to contact carrier 35.

Circuit breaker 10 also includes an automatic'tripping mechanism 100 and a quick make-break toggle operating mechanism 32. Operating mechanism 32 is connected to the contacts of all three phases by means of a transverse insulating tiebar 33, with U-shaped straps 34 connecting the respective contact carriers 35 to the common tiebar 33. Carrier 35 is pivotally mounted at 45 to suitable bearings in the operating mechanism frame 47. Mounting frame 47 includes ears 84 which receive screw members 49 for securement to circuit breaker base embossment 50.

The center phase carrier 35 is connected at its pivot rod 36 to the lower of the operating mechanism toggle linkage 37-38, with the toggle links joined at knee 39. Knee 39 includes a pivotally mounted plate member 40 to which the circuit breaker operating springs, shown as a pair 41-41 are connected at one end 42-42 thereof. The other ends 43-43 are located in suitable apertures with the operating handle frame 45, such that the operating springs 45-45 are in over-center relationship with respect to toggle linkage 37-38. The lower end of handle frame member 45 is pivotally mounted to bosses $3 of operating mechanism frame 47. Operating handle 80 is mounted to upstanding posts 81 of frame member 45.

The operating mechanism 32 also includes a cradle connected latch tip 51 in engagement with bracket extension 52 of the trip assembly 100. Bracket extension 52 is coupled to tripper bar 53 so as to effect tripping disengagement of latched members 51, 52 upon counter-clockwise movement of tripper bar 53. Such counter-clockwise movement may be effected by the engagement of elongated bimetallic member 54 and tripper bar adjustment screw 55 or the downward movement of the instantaneous trip plunger rod 56 with the accompanying engagement of adjustable screw head 57 and tripper extension 58 with adjustment of the instantaneous trip being provided by button 59. I l

The movable contact arm mounting may include ind! vidual adjusting studs 60 to establish the open gap circuit position of contacts 24-25 relative to stationary contacts 22-23 as shown in the open position of FIGURE 3; as well as a contact pressure adjustment means shown as 71; as is the subject of copending US. patent application Serial No. 430,549, filed February 5, 1965, in the name of Carl E. Gryctko and entitled Circuit Breaker Contact Mounting.

The trip unit assembly includes a terminal strap 102 for each of the phases. Terminal straps 102 include apertures 104 at one end thereof to mate with cooperating aperture 106 of the load terminal strap 21 for electrical and mechanical securement thereto. The opposite end of terminal strap 102 includes aperture 108 which similarly mate with cooperating aperture 110 of the contact carrier strap29. Bolt means 112' extend through cooperating apertures 104, 106 at the load end of the aircuit breaker frame, with similar bolt means 114 extend= ing through cooperating apertures 108, 110 for mounting each of the terminal straps 102 of the trip unit assembly 100 to their respective load terminal straps 21 and contact carrier straps 29. It should be understood at this point that normal manufacturing tolerances between the trip unit asembly mounting apertures 104, 108 and the cooper: ating conducting members 21, 29 of the circuit breaker frame will result in some anticipated degree of rnis'a'lignmerit between the mounting of the terminal strap 102 m the circuit breaker frame. Such misalignment will dc velop stress forces. It is quite important that means he provided to prevent such stress forces from being transmitted to the elongated thermally responsive bimetallic member 54, where it will result in a change in overload calibration. To provide some compensation, the lower end of the bimetallic member 54, which is sec-urably mounted to frame assembly 112 by the transverse bracket member 114 is connected to the terminal strap 102 'via a flexible thermal shunt 118 formed of a successive plurality of copper laminates, as is the subject of above mentioned US. Patent No. 3,139,497. In accordance with my invention an additional spacer member 120 formed of a good thermally conductive material, such as copper, is placed intermediate the lower surface of thermal shunt 118 and the upper surface m3 of terminal strap 102.

Reference is now made to FIGURES 6 land 7 which show the mounting arrangement of bimet-al element 54- to the current carrying terminal strap of the trip unit assembly in further detail. As noted above, the lower end of elongated bimetal member 54 is securably mounted to transverse bracket member 114 as by rivets 116. The rivets 116 also securably connect the upper section 130 of the thermal shunt member 118 to the bimetallic member so as to provide both a good mechanical and thermally conductive connection therebetween. The outermost extreme ends of transverse bracket member 114 includes tapped apertures 125 which receive screw members 126 for securably mounting the bimetallic element to the frame member 112 of the trip unit assembly. The opposite end section 132 of the thermal shunt 118 is securably mounted to the upper surface 103 of terminal strap M92 as by rivet members 134. The spacer member 120 of the instant invention is interposed between end 132 of the thermal shunt and the upper surface 103 of the terminal strap. Spacer 120 provides a gap d between the lower surface of the thermal shunt, intermediate section 131, and the upper surface 193 of the terminal strap, to permit increased flexing of the thermal shunt. Particularly, the gap between the thermal shunt 118 and bus bar 102, at the bend 138, allows for vertical misalignment as shown dotted in FIGURE 6.

Another plate member 136 may also be placed against the opposite surface of the thermal shunt section 132 to facilitate the riveting operation. Aperture 145 is also shown vertically extending through section 132 of the thermal shunt, spacer plate 120, upper plate 136, and terminal strap 102. This aperture is provided in this embodiment for accommodating the plunger rod 56 of the instantaneous trip.

The thermal shunt intermediate portion 131 joins the end sections 130-132 by an angular bend 138 such that the end sections 130-132 are angularly disposed with respect to each other and lie in substantially perpendicular planes. Such perpendicularity corresponds to there being an exact alignment between the mounting apertures 104, 108 of the terminal strap and cooperating apertures 106, 110 of the circuit breaker frame. Should there be any misalignment, as shown, for example, by the dotted lines of FIGURE 7, the angular disposition between sections 13i}132 will vary from such a perpendicular relationship, as provided by the relief of flexible shunt member 118 and spacer member 12% so as to prevent the transmission of the stress forces to elongated bimetallic member 54.

It is therefore seen that the instant invention provides an improved interconnection between the thermally responsive bimetallic member of a replaceable trip unit assembly and the current carrying strap thereof such that increased compensation for misalignment will be provided to prevent a change in the circuit breaker calibration. It should be further recognized that a substantially increased degree of compensation over that shown in aforementioned United States Patent No. 3,139,497 is provided by the addition only of an ineXpensive spacer member.

Though I have described a preferred embodiment of my novel invention, many variations and modifications will now be obvious to those skilled in the :art and I prefer therefore to be limited not by the specific disclosure herein but only by the appended claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

1. A circuit breaker comprising a housing having mounted thereto at least one pair of cooperating contacts, operating means for moving said contacts between an engaged and disengaged position; latch means cooperating with said operating means for maintaining said contacts in their engaged position under normal load conditions, a trip unit including cur-rent sensing means operatively responsive to the current flow through the circuit, and including means for releasing said latch means responsive 6 to predetermined overload conditions, means for remova'bly mounting said trip unit as an integral assembly to said circuit breaker housing, such that said circuit breaker accommodates various trip unit assemblies, said trip unit including a rigid terminal strap for securement to cooperating current carrying members carried by said circuit breaker housing, said trip unit including a mounting frame, said current sensing means including a thermally responsive element fixedly secured at a first end to said mounting frame, at a location remote from said terminal strap, a thermal shunt connecting said thermally responsive element to said terminal strap, relief means in the connection between said thermally responsive element and said rigid terminal strap for preventing transmission of stress forces to said thermally responsive element responsive to relative misalignment in the mounting of said terminal strap of the replaceable trip unit assembly to the cooperating current carrying members of the circuit breaker housing, such that the thermal calibration of said thermally responsive element is substantially independent of such stress forces, said relief means including means to compensate for misalignment derived stress forces in both a first and second direction, said first direction resulting from lateral misalignment between said terminal strap and the cooperating current carrying members of the circuit breaker, said second direction resulting from vertical misalignment between said terminal strap and the cooperating current carrying members of the circuit breaker.

2. A circuit breaker comprising a housing having mounted thereto at least one pair of cooperating contacts, operating means for moving said contacts between an engaged and disengaged position, latch means cooperating with said operating means for maintaining said contacts in their engaged position under normal load conditions, a trip unit including current sensing means operatively responsive to the current flow through the circuit breaker, and including means for releasing said latch means responsive to predetermined overload conditions, means for removably mounting said trip unit as an integral assembly to said circuit breaker housing, such that said circuit breaker accommodates various trip unit assemblies, said trip unit including a rigid terminal strap for securement to cooperating current carrying members carried by said circuit breaker housing, said trip unit including a mounting frame, said current sensing means including a thermally responsive element fixedly secured at a first end to said mounting frame, at a location remote from said terminal "strap, a thermal shunt connecting said thermally responsive element to said terminal strap, relief means in the connection between said thermally responsive element and said rigid terminal strap for preventing transmission of stress forces to said thermally responsive element, responsive to relative misalignment in the mounting of said terminal strap of the replaceable trip unit assembly to the cooperating current carrying members of the circuit breaker housing, such that the thermal calibration of said thermally responsive element is substantially independent of such stress forces, said terminal strap being formed of a substantially planar member, having mounting means at the opposite ends for securement to cooperating space-separated current carrying members of the circuit breaker, said thermal shunt has a first end fixedly secured to an intermediate surface region of said terminal strap, and a second end fixedly secured to said thermally responsive element, said relief means including a thermally conductive spacer member interposed between said first end of said thermal shunt and said intermediate surface region of said terminal strap, said spacer member of predetermined dimensions to permit misalignment of up to a predetermined amount between said terminal strap and its cooperating space-separated current carrying members of the circuit breaker. i

3. A circuit breaker comprising a housing, having mounted thereto at least one pair of cooperating contacts,

operating means for moving said contacts between an engaged and disengaged position, latch means cooperating with said operating means for maintaining said contacts in their engaged position under normal load condi tions, a trip unit including current sensing means operatively responsive to the current flow through the circuit breaker, and including means for releasing said latch means responsive to predetermined overload conditions, means for removably mounting said trip unit as an integral assembly to said circuit breaker housing, such that said circuit breaker accommodates various trip unit assemblies, said trip unit including a rigid terminal strap for securement to cooperating current carrying members of said circuit breaker, said trip unit including a mounting frame, said current sensing means including a thermally responsive element fixedly secured at a first end to said mounting frame, at a location remote from said terminal strap, a thermal shunt connecting said thermally responsive element to said terminal strap, relief means in the connection between said thermally responsive element and said rigid terminal strap for preventing transmission of stress forces to said thermally responsive element responsive to relative misalignment in the mounting of said terminal strap of the replaceable trip. unit assembly to the cooperating current carrying members of the circuit breaker housing, such that the thermal calibration of said thermally responsive element is substantially independent of such stress forces, said terminal strap being formed of a substantially planar member, having mounting means at the opposite ends for securement to cooperating space-separated current carrying members of the circuit breaker, said thermal shunt having a first end fixedly secured to an intermediate surface region of said terminal strap, and a second end fixedly secured to said thermally responsive element, said relief means including a thermally conductive spacer member interposed between said first end of said thermal shunt and said intermediate surface region of said terminal strap, said spacer member of predetermined dimensions to permit misalignment up to a predetermined amount between said terminal strap and its cooperating space-separated current carrying members of the circuit breaker, and said thermal shunt formed of a flexible member, to provide additional relief means, such that said relief means compensates for misalignment derived stress forces in both a first and second direction, said first direction resulting from lateral misalignment between said terminal strap and the cooperating current carrying members of the circuit breaker, said second direction resulting from vertical misalignment between said terminal strap and the cooperating current carrying members of the circuit breaker.

4. In a circuit breaker as set forth in claim 2, said thermal shunt having an intermediate portion including first and second sections, angularly disposed with respect to each other, and meeting at a bend such that said first and second ends are lying in substantially perpendicular planes, said first section disposed substantially parallel to said terminal strap, and displaced therefrom an amount substantially corresponding to the thickness of said spacer member, said second section perpendicularly extending upwards towards said thermally responsive element, with the displacement of said first section from said terminal strap permitting a wide variation of the angular disposition between said first and second sections about a perpendicular condition, corresponding to misalignment between said terminal strap and the cooperating current carrying members of the circuit breaker.

5. In a circuit breaker as set forth in claim 3, said thermal shunt having an intermediate portion including first and second sections, angularly disposed with respect to each other, and meeting at a bend such that said first and second ends are lying in substantially perpendicular planes, said first section disposed substantially parallel to said terminal strap and displaced therefrom an amount substantially corresponding to the thickness of said spacer member, said second section perpendicularly extending upwards towards said thermally responsive element, with the displacement of said first section from said terminal strap permitting a wide variation of the angular disposition between said first and second sections about a perpendicular condition, corresponding to misalignment between said terminal strap and the cooperating current carrying members of the circuit breaker.

6. A multiphase circuit breaker including a housing, having mounted thereto at least one pair of cooperating contacts for each phase, a contact operating means for moving said contacts between an engaged and disengaged position, latch means cooperating with said operating means for maintaining said contacts in their engaged position under normal load conditions, a trip unit including current sensing means for each phase responsive to the phase current, and including means for releasing said latch means responsive to predetermined overload conditions, means for removably mounting said trip unit as an integral assembly to said circuit breaker housing, such that said circuit breaker accommodates various trip assemblies, said trip unit including a rigid terminal strap for each phase for securement to cooperating phase current carrying members of said circuit breaker, each of the individual phase members of said trip unit including a mounting frame, said current sensing means including a thermally responsive element fixedly secured at a first end to said mounting frame, at a location remote from said terminal strap, a thermal shunt connecting said thermally responsive element to said terminal strap, relief means in the connection between said thermally responsive element and said rigid strap for preventing transmission of stress forces to said thermally responsive element responsive to relative misalignment in the mounting of said terminal strap of the replaceable trip unit assembly to the cooperating current carrying members of the circuit breaker housing, such that the thermal calibration of said thermally responsive element is substantially independent of such stress forces, said relief means including means to compensate for misalignment derived stress forces in both a first and second direction, said first direction resulting from lateral misalignment between said terminal strap and the cooperating current carrying members of the circuit breaker, said second direction resulting from vertical misalignment between said terminal strap and the cooperating current carrying members of the circuit breaker.

7. A multiple circuit breaker including a housing, having mounted thereto at least one pair of cooperating contacts for each phase, a contact operating means for moving said contacts between an engaged and disengaged position, latch means cooperating with said operating means for maintaining said contacts in their engaged position under normal load conditions, a trip unit including current sensing means for each phase responsive to the phase current, and including means for releasing said latch means responsive to predetermined overload conditions, means for removably mounting said trip unit as an integral assembly t said circuit breaker housing, such that said circuit breaker accommodates various trip unit assemblies, said trip unit including a rigid terminal strap for each phase for securement to cooperating phase current carrying members of said circuit breaker, said trip unit including a mounting frame, said current sensing means including a thermally responsive element fixedly secured at a first end to said mounting frame, at a location remote from said terminal strap, a thermal shunt connecting said thermally responsive element to said terminal strap, relief means in the connection between said thermally responsive element and said rigid terminal strap for preventing transmission of stress forces to said thermally responsive element responsive t relative misalignment in the mounting of said terminal strap of the replaceable trip unit assembly to the cooperating current carrying members of the circuit breaker housing, such that the thermal calibration of said thermally responsive element is substantially independent of such stress forces, said terminal strap being formed of a substantially planar member, having mounting means at the opposite ends for securement to cooperating space-separated current carrying members of the circuit breaker, said thermal shunt having a first end fixedly secured to an intermediate surface region of said terminal strap, and a second end fixedly secured t said thermally responsive element, said relief means including a thermally conductive spacer member interposed between said first end of said thermal shunt and said intermediate surface region of said terminal strap, said spacer member of predetermined dimensions to permit misalignment of up to a predetermined amount between said terminal strap and its cooperating space-separated current carrying member of the circuit breaker.

8. In a multiphase circuit breaker as set forth in claim 7, said thermal shunt having an intermediate portion including first and second sections, angularly disposed with respect to each other, and meeting at a bend such that said first and second ends are lying in substantially perpendicular planes, said first section disposed substantially parallel to said terminal strap and displaced therefrom an amount substantially corresponding to the thickness of said spacer member, said second section perpendicularly extending upwards towards said thermally responsive element, with the displacement of said first section from said terminal strap permitting a wide variation of the angular disposition between said first and second sections about a perpendicular condition, corresponding t misalignment between said terminal strap and the cooperating current carrying members of the circuit breaker.

9. A multiphase circuit breaker including a housing, having mounted thereto at least one pair of cooperating contacts for each phase, a contact operating means for moving said contacts between an engaged and disengaged position, latch means cooperating with said operating means for maintaining said contacts in their engaged position under normal load conditions, a trip unit including current sensing means for each phase responsive to the phase current, and including mean-s for releasing said latch means responsive to predetermined overload conditions, means for removably mounting said trip unit as an integral assembly to said circuit breaker housing, such that said circuit breaker accommodates various trip unit assemblies, said trip unit including a rigid terminal strap for each phase for securement to cooperating phase current carrying members of said circuit breaker, said trip unit including a mounting frame, said current sensing means including a thermally responsive element fixedly secured at a first end to said mounting frame, at a location remote from said terminal strap, a thermal shunt connecting said thermally responsive element to said terminal strap, relief means in the connection between said thermally responsive element and said rigid terminal strap for preventing transmission of stress forces to said thermally responsive element responsive to relative misalignment in the mounting of said terminal strap of the replaceable trip unit assembly to the cooperating current carrying members of the circuit breaker housing, such that the thermal calibration of said thermally responsive element is substantially independent of such stress forces, said terminal strap being formed of a substantially planar member, having mounting means at the opposite ends for securement to cooperating spaceseparated current carrying members of the circuit breaker, said thermal shunt having a first end fixedly secured to an intermediate surface region of said terminal strap, and a second end fixedly secured to said thermally responsive element, said relief means including a thermally conductive spacer rnem'ber interposed between said first end of said thermal shunt and said intermediate surface region of said terminal strap, said spacer member of predetermined dimensions to permit a misalignment up to a predetermined amount between said terminal strap and its cooperating space-separated current carrying member of the circuit breaker, and said thermal shunt formed of a flexible member, to provide additional relief means, such that said relief means compensate for misalignment derived stress forces in both a first and second direction, said first direction resulting from lateral misalignment between said terminal strap and the cooperating current carrying members of the circuit breaker, said second direction resulting from vertical misalignment between said terminal strap and the cooperating current carrying members of the circuit breaker.

10. In a multiphase circuit breaker as set forth in claim 9, said thermal shunt having an intermediate portion including first and second sections, angularly disposed with respect to each other, and meeting at a bend such that said first and second ends are lying in substantially perpendicular planes, said first section disposed substantially parallel to said terminal strap, and displaced therefrom an amount substantially corresponding to the thickness of said spacer member, said second section perpendicularly extending upwards towards said thermally responsive element, with the displacement of said first section from said terminal strap permitting a wide variation of the angular disposition between said first and second section about a perpendicular condition, corresponding to misalignment between said terminal strap and the cooperating current carrying members of the circuit breaker.

References Qited by the Examiner UNITED STATES PATENTS 2,050,284 8/1936 Dorfman 200116 2,416,163 2/1947 Dwyer et al, 2,653,202 9/ 1953 Cole. 3,125,653 3/1964 Cole et al. 200-116 3,136,921 6/1964 Dorfman et al. 200116 X 3,139,497 6/ 1964 Giessner. 3,162,739 12/1964 Klein et al 200116 X 3,213,220 1 0/1965 Powell 2001 16 X BERNARD A. GILH-EANY, Primary Examiner. H. B. GILSON, Assistant Examiner. 

1. A CIRCUIT BREAKER COMPRISING A HOUSING HAVING MOUNTED THERETO AT LEAST ONE PAIR OF COOPERATING CONTACTS, OPERATING MEANS FOR MOVING SAID CONTACTS BETWEEN AN ENGAGED AND DISENGAGED POSITION; LATCH MEANS COOPERATING WITH SAID OPERATING MEANS FOR MAINTAINING SAID CONTACTS IN THEIR ENGAGED POSITION UNDER NORMAL LOAD CONDITIONS, A TRIP UNIT INCLUDING CURRENT SENSING MEANS OPERATIVELY RESPONSIVE TO THE CURRENT FLOW THROUGH THE CIRCUIT, AND INCLUDING MEANS FOR RELEASING SAID LATCH MEANS RESPONSIVE TO PREDETERMINED OVERLOAD CONDITIONS, MEANS FOR REMOVABLY MOUNTING SAID TRIP UNIT AS AN INTEGRAL ASSEMBLY TO SAID CIRCUIT BREAKER HOUSING, SUCH THAT SAID CIRCUIT BREAKER ACCOMMODATES VARIOUS TRIP UNIT ASSEMBLIES, SAID TRIP UNIT INCLUDING A RIGID TERMINAL STRAP FOR SECUREMENT TO COOPERATING CURRENT CARRYING MEMBERS CARRIED BY SAID CIRCUIT BREAKER HOUSING, SAID TRIP UNIT INCLUDING A MOUNTING FRAME, SAID CURRENT SENSING MEANS INCLUDING A THERMALLY RESPONSIVE ELEMENT FIXEDLY SECURED AT A FIRST END TO SAID MOUNTING FRAME, AT A LOCATION REMOTE FROM SAID TERMINAL STRAP, A THERMAL SHUNT CONNECTING SAID THERMALLY RESPONSIVE ELEMENT TO SAID TERMINAL STRAP, RELIEF MEANS IN THE CONNECTION BETWEEN SAID THERMALLY RESPONSIVE ELEMENT AND SAID RIGID TERMINAL STRAP FOR PREVENTING TRANSMISSION OF STRESS FORCES TO SAID THERMALLY RESPONSIVE ELEMENT RESPON- 